This invention relates to a robot arm device which is capable of conveying an article such as wafer in circumferential and radial directions.
There have been proposed a number of robot arm devices. In the Japanese magazine "ELECTRONIC MATERIAL", August, 1991, for example, a robot arm device shown in FIG. 8 is disclosed. This robot arm device is employed in a conveying apparatus for conveying wafers as material of semiconductor memories to a specified processing section.
This conventional robot arm device basically includes a base portion 20, a base drum 310 rotatably supported on the base portion 20, and an arm portion 10. The arm portion 10 mainly consists of an arm member 110, a forearm member 120, and a hand member 130. These members are rotatably connected with one another. The hand member 130 is adapted for carrying or gripping a wafer at its leading end, and is enabled to make a linear movement.
The robot arm device is further provided with a drum drive motor 40 for changing the circumferential position of the hand member 130 and an arm drive motor 50 for changing the radial position of the hand member 130, that is, linear movement of the hand member 130.
Specifically, a support shaft 440 extends vertically upward substantially from a center of the base portion 20. A vertically long pulley 430 is mounted rotatably about the support shaft 440. An axis of the support shaft 440 agrees with an axis of the base drum 310. The pulley 430 is fixedly attached with a bottom portion of the base drum 310. Accordingly, the base drum 310 is rotatable about the axis of the support shaft 440. At a center of a top portion of the base drum 310 is fixedly attached a transmission pulley 360. An axis of the transmission pulley 360 agrees with the axis of the base drum 310. The stationary pulley 360 is rotatable together with the base drum 310.
The drum drive motor 40 is mounted on the base portion 20, and an output pulley 420 is mounted on an output shaft 410 of the drum drive motor 40. Another transmission shaft 450 extends vertically upward from the base portion 20, and pulleys 450 and 460 are mounted rotatably on the transmission shaft 450. A drive belt 60 is mounted between the output pulley 420 and the pulley 460 and a belt 610 is mounted between the pulley 470 and the pulley 430.
The arm drive motor 50 is mounted on an outer periphery of the base drum 310, and an output pulley 520 is securely mounted on an output shaft 510 of the arm drive motor 50. A bracket 580 is fixedly attached on the base drum 310 at a position opposed to the arm drive motor 50. A transmission shaft 550 is mounted on the bracket 580 rotatably about its longitudinal axis. Pulleys 560 and 570 are mounted on the transmission shaft 550.
An arm drive shaft 340 extends along the axis of the base drum 310. The arm drive shaft 340 is rotatable independently from the base drum 310 and the transmission pulley 360. Specifically, an upper portion of the arm drive shaft 340 projects upward through the top portion of the base drum 310. An arm drive pulley 530 corresponding to the pulley 570 is mounted at the bottom end of the arm drive shaft 340, and windows 590 are formed in the periphery wall of the base drum 310 at positions opposed to the pulleys 530 and 570. A drive belt 70 is mounted between the drive pulley 520 and the pulley 560, and a belt 710 is mounted between the pulleys 570 and 530 through the windows 590.
A top of the arm drive shaft 340 is fixedly attached with a base end of the arm member 110. At a leading end of the arm member 110, a forearm drive shaft 350 which extends in parallel with the arm drive shaft 340 is mounted through the arm member 110 in such a way that the forearm drive shaft 350 is rotatable independently from the arm member 110. A forearm drive pulley 370 is integrally mounted at a bottom end of the forearm drive shaft 350. An intermediate stationary pulley 380 is fixedly attached on the arm member 110. It should be noted that the forearm drive shaft 350 is independent from the stationary pulley 380. An axis of the intermediate stationary pulley 380 agrees with the axis of the forearm drive shaft 350.
A base end of the forearm member 120 is fixedly mounted on an upper end of the forearm drive shaft 350, and a hand drive shaft 330 which extends in parallel with the forearm drive shaft 350 is mounted at a leading end of the forearm member 120. The hand drive shaft 330 extends through the forearm member 120 in such a way that the hand drive shaft 330 is rotatable independently from the forearm member 120. A hand drive pulley 390 is integrally mounted at a bottom end of the hand drive shaft 330 and the hand member 130 is integrally mounted at an upper end of the hand drive shaft 330.
The distance between an axis of the arm drive shaft 340 and an axis of the forearm drive shaft 350 is set to be the same as that between the axis of the forearm drive shaft 350 and an axis of the hand drive shaft 330.
A first belt 3670 is mounted between the stationary and forearm drive pulleys 360 and 370, and a second belt 3890 is mounted between the intermediate stationary and hand drive pulleys 380 and 390.
The ratio of the diameter of the transmission pulley 360 to that of the forearm drive pulley 370 is set at 2:1 and the ratio of the diameter of the intermediate stationary pulley 380 to that of the hand drive pulley 390 is set at 1:2.
When changing the circumferential position of the hand member 130 or rotating the arm portion 10, the drum drive motor 40 is driven while the arm drive motor 50 is suspended. Specifically, a torque of the drum drive motor 40 which is driven in a clockwise or counterclockwise direction is transmitted to the base drum 310 by the way of the output shaft 410, pulley 420, belt 60, pulley 460, pulley 470, belt 610, and the pulley 430, thereby rotating the base drum 310 in a clockwise or counterclockwise direction. The base drum 310 integrally carries the arm portion 10, the arm drive motor 50, and the other parts. Accordingly, the clockwise or counterclockwise rotation of the base drum 310 rotates the arm portion 10 in a clockwise or counterclockwise direction.
When changing the radial position of the hand member 130 or straightly moving the hand member in radial directions, on the other hand, the arm drive motor 50 is driven while the drum drive motor 40 is suspended. A torque of the arm drive motor 50 which is driven in a specified direction is transmitted to the arm drive pulley 530 by the way of the output shaft 510, the output pulley 520, the drive belt 70, the pulley 560, the transmission shaft 550, the pulley 570, and the belt 710, and further transmitted to the arm member 110 by the way of the arm drive shaft 340.
In the case of contracting the arm portion 10, in other words, moving the hand member 130 inward, the arm drive motor 50 is driven in a clockwise direction, and the arm member 110 is rotated in a clockwise direction, the forearm drive shaft 350 moves in a clockwise direction about the axis of the arm drive shaft 340, and at the same time the forearm drive pulley 370 rotates in a counterclockwise direction.
Specifically, the contact portions of the first belt 3670 with the stationary and forearm drive pulley 360 and 370 shift in a counterclockwise direction with the clockwise rotation of the arm member 110. In this time, however, the transmission pulley 360 does not rotate together with the rotation of the arm member 110 because of being fixedly attached on the base drum 310 and independent from the arm drive shaft 340. Accordingly, the counterclockwise shift of the contact portions of the first belt 3670 will cause the forearm drive shaft 350 to rotate in a counterclockwise direction. The counterclockwise rotation of the forearm drive shaft 350 is twice faster than the rotation of the arm member 110 because the diameter of the forearm drive pulley 370 is a half of that of the transmission pulley 360.
Consequently, the forearm member 120 rotates in a counterclockwise direction about the axis of the forearm drive shaft 350 twice faster than the arm member 110. In similar to the rotation of the arm member 110, the counterclockwise rotation of the forearm member 120 causes a clockwise shift of the second belt 3890 because the intermediate stationary pulley 380 is fixedly attached to the arm member 110 and does not rotate together with the forearm member 120. This shift of the second belt 3890 causes a clockwise rotation of the hand drive pulley 390, the hand drive shaft 330, and the hand member 130. The hand member 130 rotates in a clockwise direction at an angular speed half of that of the forearm member 120 because the diameter of the hand drive pulley 390 is twice greater than that of the intermediate stationary pulley 380.
Consequently, the combination of the clockwise rotation of the arm member 110, the double angular speed counterclockwise rotation of the forearm member 120, and the clockwise rotation of the hand member 130 will straightly move the hand member 130 in an inward radial direction.
In the case of expanding the arm portion 10, i.e., moving the hand member 130 outward, the arm drive motor 50 is driven in a counterclockwise direction. Thereafter, each part moves in the reverse direction to the contraction of the arm portion 10, and the hand member 130 will be straightly moved in an outward direction.
in this conventional robot arm device, the expansion and contraction of the arm portion 10 is executed only by the use of the arm drive motor 50. The forearm member 120 and the hand member 130 are rotated owing to the relative shift of the first and second belts 3670 and 3890. Also, the double speed rotation of the forearm member 120 is attained by the half diameter of the forearm drive pulley 370 relative to the transmission pulley 360.
Accordingly, the forearm drive shaft 370 produces the rotating force to rotate the forearm member 120 carrying the hand member 130 not much than a half comparing to a belt mechanism where the forearm drive shaft 370 would have a diameter equal to or greater than the transmission pulley 360. It will be seen that to rotate the forearm member 120 carrying the hand member 130, a considerable big torque is necessary. It is impossible to increase the diameter of the forearm drive pulley 370 because of the radial straight movement. Accordingly, there is no way but increasing the output torque of the arm drive motor 50 to raise the forearm member rotating torque, which needs a more expensive motor. Thus, the production costs will rise.
Also, the forearm drive pulley 370 whose diameter is smaller than the stationary pulley 360 has smaller belt contact area than the stationary pulley 360. A slippage will be likely to occur between the forearm drive pulley 370 and the belt 3670. This will also reduce the torque to rotate the forearm member 120.
Further, it will be apparent that the radial straight movement of the hand member 130 is accomplished by a very finely accurate geometric combination of the arm members, shaft, pulleys, and belts. If there is a dimensional error in one part, it will be impossible to attain the accurate straight radial movement. However, it is impossible to perfectly machine each part into a theoretically required dimension. Accordingly, there is no way but allowing some error or displacement. Also, long use of this device results in some mechanical deformations, and consequently increase such error. Accordingly, there has been the long demand of solving this problem.
Furthermore, in this robot arm, the arm portion 10 is rotated in a circumferential direction by rotating the base drum 310 carrying the arm portion 10 and the arm drive motor 50 with the drum drive motor 40. Accordingly, a considerable big load is applied to the drum drive motor 40. This needs a motor capable of generating a great torque, and then raise the production costs.
Japanese Unexamined Utility Model Publication No. 62-150087 discloses another robot arm device whose construction is basically identical to that of the above-mentioned robot arm device. However, circumferential movement or rotation of an arm portion is accomplished by rotating both an arm member and a forearm member carrying a hand member at a timed relation with each other, instead of rotating of the base drum 310 carrying the arm drive motor 50 and the arm portion 10 as mentioned in the above-mentioned robot arm device.
Specifically, there is provided a forearm driving mechanism in addition to an arm driving mechanism. The arm driving mechanism is substantially identical to that of the above-mentioned robot arm device which mainly consists of the arm drive motor 50 and the arm drive shaft 340 fixedly attached with the arm member 110.
The forearm driving mechanism includes a forearm drive motor, an output shaft of the motor, a first output pulley fixedly attached to the output shaft, a first transmission pulley driving connected with the first output pulley by belt, and a second transmission pulley driving connected with a forearm drive pulley by a belt.
The second transmission pulley is equivalent of the transmission pulley 360 of the above robot arm device. The second transmission pulley is fixedly connected with the first transmission pulley. An axis of these transmission pulleys agrees with an axis of the arm drive shaft. The diameter of the first and second transmission pulleys is twice greater than that of the forearm drive pulley, and also twice greater than that of the output pulley.
Further, on the output shaft of the forearm drive motor is fixedly attached a second output pulley. On the output shaft of the arm drive motor, on the other hand, is fixedly attached a third transmission pulley. The second output pulley is drivingly connected with the third transmission pulley. The second output pulley has the same diameter as the first output pulley and the third transmission pulley has the same diameter as the first and second transmission pulleys. Accordingly, the diameter ratio between the second output pulley and the third output pulley is 1:2.
In this robot arm device, when the entirety of the arm portion is rotated in a circumferential, the forearm drive motor is driven while the arm drive motor is suspended. A torque of the forearm drive motor is transmitted to the arm member by one way of the output shaft, second output pulley, and arm drive shaft. This torque transmission rotates the arm member carrying the forearm and hand member in a direction identical to that of the forearm drive motor at an angular speed half of that of the forearm drive motor.
Also, the torque of the forearm drive motor is transmitted to the forearm member by one way of the output shaft, first output pulley, first and second transmission pulley, and forearm drive pulley. This torque transmission rotates the forearm member carrying the hand member in a direction identical to that of the forearm drive motor and the arm member. In this case, the forearm drive pulley receives a torque which would rotate the forearm member in the identical direction twice faster than the forearm member. However, the half angular speed rotation of the arm member cause a half angular counter rotation due to the relative shift of the belt. Accordingly, the forearm member will not rotate with respect to the arm member. In this way, the arm member is rotated in a circumferential direction without any expansion or contraction of the arm portion.
Comparing to the above-mentioned robot arm device, this robot arm device is advantageous in the aspect of loads applied to a motor for rotating an arm portion in a circumferential direction. Specifically, the mechanism of rotating the base drum 310 carrying the arm drive motor 50 and the arm portion 10 is replaced with the mechanism of rotating the arm member and the forearm member carrying the hand member. In other word, the drum drive motor 40 is replaced with the forearm drive motor.
However, this robot arm device is provided with the forearm drive pulley whose diameter is half smaller than that of the second transmission pulley. Also, the straight radial movement of the hand member is performed by the arm drive motor only. The problems which there have been in the above-mentioned robot arm device have not yet solved.